This invention relates generally to a process of thermally cracking a heavy hydrocarbon oil. More specifically, the present invention is directed to a process for the conversion of a heavy hydrocarbon oil into a light hydrocarbon oil and a pitch which is useful as a fuel by a continuous, multi-stage thermal cracking treatment.
A variety of techniques have been hitherto proposed for treating heavy hydrocarbon oils to obtain utilizable products. The thermal cracking is one such technique applicable to heavy petroleum fractions such as vacuum residues. U.S. Pat. No. 3,928,170 discloses a process, generally called Eureka process, in which a gaseous heat transfer medium is brought into direct contact with a heavy hydrocarbon oil for effecting the thermal cracking under relatively mild conditions and for stripping volatile cracked products to leave a pitch. The pitch product obtained by the Eureka process has a high content of resin components which are soluble in quinoline but insoluble in benzene, a low content of coke, a high content of aromatic components and a H/C atomic ratio of 1.0 or less and is useful as a binder for manufacturing coke and refractory materials. One problem encountered in the Eureka process is that the process is unavoidably operated in a semibatch mode because otherwise it is very difficult to prevent the occurrence of a coking during the thermal cracking of heavy hydrocarbon oils. Another problem is that the cracked hydrocarbon product has relatively a large amount of heavy hydrocarbon components and, therefore, is less valuable than light hydrocarbon oils.